10 Productivity and Food Webs in the Sea. Notes for Marine Biology: Function, Biodiversity, Ecology By Jeffrey S. Levinton

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1 10 Productivity and Food Webs in the Sea Notes for Marine Biology: Function, Biodiversity, Ecology By Jeffrey S. Levinton

2 Microbial Loop 2 Larger consumers Microbial loop DOC & POC Viruses Bacteria Herbivores Phytoplankton DIOC and nutrients Microconsumers DOC=dissolved organic carbon POC=particulate organic carbon DIOC=dissolved inorganic carbon

3 Productivity vs biomass Biomass the mass of living material present at any time, expressed as grams per unit area or volume = standing stock Productivity is the rate of production of living material per unit time per unit area or volume

4 Productivity Primary productivity - productivity due to Photosynthesis Secondary productivity - productivity due to consumers of primary producers

5 Food Chain Food chain - linear sequence showing which organisms consume which other organisms, making a series of trophic levels Food web - more complex diagram showing feeding relationships among organisms, not restricted to a linear hierarchy

6 Source: ifaw.orgl Northwest Atlantic Food Web - need simplification for analysis

7 Food Chain Abstraction North Sea trophic interactions

8 Transfer Between Trophic Levels Transfer from one trophic level to the next is not complete: 1. Some material not eaten 2. Not all eaten is converted with 100% efficiency 3. Metabolic costs are a loss

9 Transfer Between Trophic Levels 2 Budget for ingested food (use energy units): I = E + R + G I amount ingested E amount egested (loss) R amount respired (loss) G growth (partitioned between somatic growth and reproduction) (gain)

10 Transfer Between Trophic Levels 3 Incomplete transfer up a food chain: Measure by food chain efficiency: E = amount extracted from a trophic level amount of energy supplied to that level E can be as little as 10%, but as much as 50%

11 Transfer Between Trophic Levels 4 Given several trophic levels (e.g., L 1, L 2, L 3 ), Use food chain efficiency to calculate energy available to highest trophic level: L 3 P = BE n n=2 P = production at highest level B = primary production B E = food chain efficiency n = number of links between trophic levels L 2 L 1 E 2 E 1

12 Transfer Between Trophic Levels 4 Use food chain efficiency to calculate energy available to highest trophic level: P = BE n Let B = 1, E = 0.1 If n = 2, P =? L 3 L 2 L

13 Transfer Between Trophic Levels 4 Use food chain efficiency to calculate energy available to highest trophic level: P = BE n Let E = 0.1, B = 1, If n = 2, P =? P = 1 x (0.1) 2 = 1 x 0.01 = 0.01 L 3 L L 1 0.1

14 Transfer Between Trophic Levels 4 Use food chain efficiency to calculate energy available to highest trophic level: P = BE n Let E =.1, B = 1, If n = 3, P =? P = 1 x (0.1) 3 = 1 x 0.1 x 0.1 x 0.1 = 0.001

15 Transfer Between Trophic Levels 4 Use food chain efficiency to calculate energy available to highest trophic level: P = BE n Let E =.1, B = 1, If n = 5, P =? P = 1 x (0.1) 3 = 1 x 0.1 x 0.1 x 0.1x.1 =

16 Transfer Between Trophic Levels 5 Use food chain efficiency to calculate energy available to highest trophic level: P = BE n With 5 trophic levels, a change of E from 0.1 to 0.2 magnifies P by a factor of 16

17 Oceanic Food Webs Food webs in the water column of oceans vary: 1.Primary productivity (e.g., upwelling vs gyre center) 2. Food chain efficiency 3. Number of trophic levels 4. Area of ocean covered

18 Oceanic Food Webs Food Chain Type Primary Productivity gcm -2 y -1 Trophic Levels Food Chain Efficiency Potential Fish Production mgcm -2 y -1 Oceanic Shelf Upwelling ,000 Ryther 1969, Science 166: 72-76

19 Oceanic North Sea

20 Large-numbered food chains: unstable Food chains Food chain structure: Bottom up control: control of food chain by amount of primary production (leads to previous calculations we made) Top-down control: control of food chain by variation in top predators Food Chain structure: Three-level food chains: Remove top level (carnivore) and herbivore increases, resulting in low population size of primary producer. Even-numbered food chains: Primary producers tend to be rare - think about why and when

21 Measuring Primary Productivity Gross primary productivity GPP - total carbon fixed during photosynthesis. Net primary productivity NPP - total carbon fixed during photosynthesis minus that part which is respired NPP is what is available to higher trophic levels.

22 Measuring Primary Productivity Oxygen technique - Principle - relies upon fact that oxygen is released during photosynthesis CO 2 + 2H 2 O ---> (CH 2 O) n + H 2 O + O 2

23 Measuring Primary Productivity Oxygen technique - there is an addition from photosynthesis and a subtraction from respiration

24 Measuring Primary Productivity 4 Oxygen technique - Measurement of oxygen: 1. Winkler method - chemical titration of Oxygen - oxygen reacts with Mn, OH - and iodide, ppt reacts to form tetravalent iodine, (blue), then titrate with thiosulfate to iodide, starch indicator turns clear 2. Polarographic oxygen electrode - electrons leave electrode, and reduce dissolved Oxygen, generates current at electrode ds/environ_sampling/oxygen.html

iodine, (blue), then titrate with thiosulfate to iodide, starch indicator turns clear 2.

25 Measuring Primary Productivity 4 Oxygen technique - Measurement of oxygen: 1. Winkler method - chemical titration of Oxygen - oxygen reacts with Mn, OH - and iodide, ppt reacts to form tetravalent iodine, (blue), then titrate with thiosulfate to iodide, starch indicator turns clear 2. Polarographic oxygen electrode - electrons leave electrode, and reduce dissolved Oxygen, generates current at electrode ds/environ_sampling/oxygen.html

26 Measuring Primary Productivity Oxygen technique - Light-Dark bottle technique: After a time Light = oxygen from photosyn. minus resp. Dark = respiration only L-D = (PS - R) - (- R) = PS (gross) { L { D

NPP = net primary production GPP in carbon

during photysynthesis (= 1 for sugars); RQ

27 NPP = net primary production GPP in carbon units GPP gross primary production PQ photosynthetic quotient: molecules of oxygen liberated/molecules of carbon assimilated during photysynthesis (= 1 for sugars); RQ respiratory quotient X = depth, 375 conversion constant: oxygen to carbon

reporter; Must correct for diffusion of oxygen

28 Field oxygen technique Polarographic oxygen electrode placed in water column, with automated reporter; Must correct for diffusion of oxygen to and from atmosphere Oxygen increases only in daytime

β decay Measuring Primary Productivity Radiocarbon technique Method: add known amount of 14 C-labeled bicarbonate to solution with phytoplankton After a time: filter phytoplankton,

29 β decay Measuring Primary Productivity Radiocarbon technique Method: add known amount of 14 C-labeled bicarbonate to solution with phytoplankton After a time: filter phytoplankton, and do counts of 14 C-emitted β particles in a scintillation counter Know proportion of 14 C in total bicarbonate, which allows calculation of total carbon removed by cells from solution

30 Measuring Primary Productivity Radiocarbon technique - Correction: 14 C is taken up more slowly than much more common stable isotope 12 C. Therefore, --> need to multiply results by 1.05 to get amount in photosynthesis

31 14 C method R L counts in light bottle R D counts in dark bottle W total bicarbonate in water R count expected from total 14 C added to container N time 1.05 partition of 14C relative to 12C

32 Measuring Primary Productivity Compare Oxygen technique with radiocarbon: Oxygen technique - used where primary production is high in estuaries, shelf Radiocarbon technique - useful where primary production is low such as open ocean, gyre centers Oxygen technique tends to give higher estimates of primary production, perhaps because cells are leaking sugars during photosynthesis, resulting in loss of radiocarbon when cells are filtered and counted

33 Measuring Primary Productivity 11 Satellite Approaches: Satellites can use photometers specific to wavelength to measure chlorophyll, Seawater temperature Need ground truthing to get relationship Between chlorophyll concentration and primary production; varies with region

35 Global data from oxygen and radiocarbon measures

36 Geographic Variation of Productivity 1. Continental shelf and open-ocean upwelling Areas are most productive 2. Convergences and fronts often are sites of rise of nutrient rich deep waters (e.g., shallow water seaward of slope 3. Central ocean, gyre centers are nutrient poor, low primary production

37 Satellite data photometer tuned to chlorophyll a

38 Some measures obtained from satellites What is measured Infrared Ocean color AMSR class microwave passive receptor high-precision altimetry Scatterometer (microwave radiation source) What is inferred SST, Sea Ice Chlorophyll SST, wind speed, sea ice Sea level anomaly from steady state Surface vector wind

39 Application to Climate Change Oscillatory changes - ENSO, NAO, etc. Global temperature change - correlations with water structure, primary production patterns - global and regional

40 El Niño thermal trace

41 Application to climate change Sea surface temperature increases: stratification increases, primary productivity decreases Behrenfeld et al Nature

42 The End

Marine Primary Productivity: Measurements and Variability. Matt Church Department of Oceanography MSB 612

Marine Primary Productivity: Measurements and Variability Matt Church Department of Oceanography MSB 612 Sunlight CO 2 + 2H 2 O CH 2 O + O 2 + H 2 O + heat Gross Primary Production (GPP): The rate of organic